Stepping through macro expansions

[deliciouslytyped]

Related to #123 ,

I want to debug the following Makefile;
the make-dirs call expands to nothing:

define _make-dir
$1/.dum: $(not-dir $1)/.dum
        mkdir $(dir $@)
        touch $(dir $@)/.dum
endef

# we dont try to create/depend on /.dum
define make-dir
$(if $(not-dir $1),$(call _make-dir,$1),)
endef

$(call make-dir,test/)

I've skimmed through the manual earlier and looked through the in-REPL documentation, maybe I'm missing something but

• I don't see any way to step through macro expansions
• I don't see a way to dump the contents of the file after expansion
• are there other techniques for debugging macros?
  Are there any existing solutions to these, or are there features that could be implemented?

[deliciouslytyped]

I'm currently trying to find a workaround by trying to write a $(call trace,...) function that can be inserted in a nested expansion, similar to trace functions in functional programming languages; it prints the value it is passed and then returns it; but I'm not very good at make programming yet.

[deliciouslytyped]

Another possibility might be to

• use the gmake guile integration
• use GDB with debug symbols enabled, if there is a function corresponding to "return the value of an expansion", and if I can find said function

[deliciouslytyped]

#125 implements the fourth (not explicitly listed previously because I thought it would be a lot harder) option: implementing the trace builtin.

However, having the ability to step through expansions would still be helpful because it doesn't require modifying the Makefile.